1. Field of the Invention
The present invention relates to a method and system for estimating total charge and air charge entering the cylinders of an internal combustion engine.
2. Description of Related Art
The mass of air, or cylinder air charge, inducted into each cylinder of an internal combustion engine must be known as precisely as possible in order to match the air mass with an appropriate mass of metered fuel. One technique involves placement of a manifold absolute pressure sensor in the intake manifold. An estimation algorithm treats the manifold absolute pressure (MAP) as an input and uses mapped engine data and engine speed to estimate air flow into the engine cylinders. For the MAP based system, gases other than air, such as intentionally introduced exhaust gas known as exhaust gas recirculation (EGR), increase the manifold pressure and should not be matched by metered fuel. However, the MAP sensor cannot distinguish between fresh air charge and EGR charge.
An object of the present invention is to provide a method and system for estimating total charge as well as air charge to cylinders of an internal combustion engine using a total charge versus MAP function that embodies air charge and EGR charge.